CTU Open Journal Systems (Czech Technical University, Prague / České vysoké učení technické v Praze)
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The influence of lithium water glass on the durability of concrete
Get PDFThe aim of the research is to verify the effect of lithium water glass on the durability and reduction of concrete absorption. For this purpose, the absorption test was made and the influence of the impregnation agent on durability when the test specimens are exposed to cyclic freezing and thawing was verified. Finally, the permeability of the test specimens was measured before and after impregnation. On the basis of the tests carried out, the effect of the impregnation agent was determined by comparing impregnated test specimens with reference specimens
Study on the reasonable RSR of arch and its influencing factors in PBA method
No full textIn this paper, based on the numerical calculation, the reasonable rise-span ratio (RSR) and its influencing factors of the arch in the PBA method are compared and analyzed, and the mechanical properties of the arch under different influencing factors (RSR, lateral pressure coefficient (LPC), and structure thickness) is further obtained. The results show that the deformation and bending moment of the arch structure decreases first and then increases with the increase of the RSR, that is, optimal RSR exists. Different LPCs have a great influence on the stress of arch structure, and the deformation and bending moment of arch structure decrease with the increase of LPC. The increase in arch structure thickness can effectively reduce structural deformation, but may also lead to an increase in structural stress due to the increase in self-weight. At the same time, the comprehensive factors show that the optimal RSR increases with the increase of LPC and structure thickness, and it is suggested that the reasonable RSR should be 0.2-0.3. The rationality of the calculation is also verified by the application status of the station RSR with the PBA method in China
Radiative Heat Transfer in Models of DC Arc Plasma
Get PDFThe radiative heat transfer in arc plasma models of a free-burning arc and a plasma torch in atmospheric pressure argon is taken into account in a self-consistent way. This is realized by the P1 method for solving the equation of radiative transfer and the multi-band approximation that considers the division of the emitted spectrum into a number of spectral bands. Net emission coefficients are evaluated by solving the equation of radiative transfer in three dimensions in an isothermal cylindrical plasma. The arc plasma parameters of the free-burning arc and the plasma torch obtained accounting for radiative transport have been compared with those from the temperature-dependent net emission coefficient for a radius of 1 mm. The results show that in general, the models applying the net emission coefficient provide results in the arc core close to that using the P1 method. The discrepancy is stronger in the arc periphery and near walls, where the P1 method predicts absorption of radiation
Semi-analytical approach-based studies of the squeeze film lubrication between rough porous annular discs: Rabinowitsch fluid model
Get PDFIn recent years, there has been much interest in the effects of porosity and surface roughness (SR) or geometric irregularities between two moving plates under hydrodynamic lubrication. Porous bearings are used extensively in wide range of equipment, including computers, office equipment, home appliances, electric motors, and vehicles. In light of the importance of the aforementioned applications, we explored how SR and porous materials affect annular discs under the condition of a squeeze film. A five-point Gauss quadrature integral formula has been used to examine the characteristics of annular discs and a small perturbation method has been used to discretise the governing Rabinowitsch fluid flow (RFF) equations. The impact of nonlinear parameters on the behaviour of porosity and SR have been visualised in terms of film pressure (FP), load carrying capacity (LCC), and squeeze response time (SRT) of annular discs. Under the conditions of pseudoplastic and dilatant fluids, the effects of SR and porous materials between annular discs have been estimated in the form of the film pressure, LCC, and SRT and are presented in this manuscript as tables and graphs. According to the findings, the performance of an annular disc is significantly affected by porous material and radial roughness patterns. In addition, when RFF is carried through a rough surface and porous media, the performance is found to improve for dilatant fluids but suffer for pseudoplastic fluids
Ecological solutions for freight trains
Get PDFThe article presents the potential of freight railway transport in terms of saving of emissions and maximizing the efficiency of operation. Attention is paid to the transport of freight trains on electrified lines with higher gradients (up to 25‰), alternatively with the possibility of a trip to non-electrified lines and sidings, which generate significant extra costs in the operation of trains and are often a reason for the carrier to deploy a locomotive of independent traction (diesel-electric) even in electrified line sections, even at the cost of increased operating costs and increased emissions. There are many such lines and possibilities of use within the Central European region and the Czech Republic.In the first part of the article, the basic categorisation of dual-mode freight locomotives and their suitability for individual operating programmes is presented. This part also describes current situation on the rolling stock market in general and directions of development taken by various locomotive manufacturers.Case studies of deployment of real freight locomotives on chosen Czech railway lines are used in the next part to present the possibilities for energy and cost savings when replacing a vehicle with independent traction by an electric or dual-mode locomotive, at least in sections equipped with overhead catenary. The pros and cons of using several possible solutions are described in detail. Further considerable savings can be achieved by, among other things, using regenerative braking and returning the generated electricity back to the catenary system when driving downhill. In this respect, however, it is also necessary to cooperate with the infrastructure manager, who must also adapt the railway lines to the operation of these vehicles.Finally, general rules for operational deployments on which the replacement of a conventional vehicle by a dual or pure electric vehicle can be considered are formulated
Proposal of operational concept for bulk substrates transport by freight trains and its application within case study of aggregate transport for construction of Vlachovice dam
Get PDFRailway freight transport represents an advantageous way for regular transport of bulk substrates. As a result of changes within the industry and energy sectors as well as in the field of consumer behaviour, such business cases decline significantly. Nevertheless, transport such of the characteristic have being (and will be) still realized however, in addition, quantities of transported goods will be known in advance – as a part of major construction or environmental remediation projects.In the period of 2020–2021, the Department of Transporting Systems in the CTU in Prague, Faculty of Transportation Sciences prepared the study “Vlára, Vlachovice Hydraulic Structure, Logistic Study of Material Transport for the Dam Construction” for the state enterprise Povodí Moravy (the Morava River Basin). Among other things, the study dealt with transport of more than 2.5 million tonnes from two quarries to the construction site of the Vlachovice dam by goods trains (the Vlachovice dam will be built in Moravia – the eastern part of the Czech Republic). It was necessary to determine an optimal route of the goods trains, their parameters and general operating concept so that the transport costs would be minimised and, concurrently, the transport performance would be as high as possible.This paper sets itself a goal to present a general procedure and principles for proposal of freight trains for a business case characterized by long-term and regular transport of large quantities of goods. For the stated case study, transport technology in the railway station Bohuslavice nad Vláří is discussed in detail
Application of ontology/conceptual modelling in the context of risk identification at level crossings
Get PDFThis conference paper discusses a new analytical approach to the evaluation of traffic safety at the railway crossings. The new method is based on the use of ontological principles. The ontological tools present a comprehensive decision-making tool, will can be applied to any potential hazardous railway crossing on a road or rail network. The ontology can be considered as a knowledge base that not only stores the data itself, but also defines the relationships between these data, and can therefore be described as a clearly suitable tool for describing risks at level crossings
Modern vehicles for regional railways
Get PDFThe paper analyses the history of two-axle rail vehicles (rail buses) used for operation on regional lines in Czechoslovakia. It also shows trends in the development of modern light autonomous rolling stocks usable for passenger transport on unprofitable regional lines in Western Europe. The measures adopted in the transport policy of the Czech Republic for the period 2021–2027 for regional railway vehicles in the Czech Republic are presented. The final part of the paper presents the results of study of the concepts of a two-axle hybrid and electric rail buses and a conceptual design of a modular solution of a partially low-floor vehicle BEMU and HEMU for passenger regional rail transport. This paper shows that it is very problematic to create a light rail vehicle (LVR) that will be economical and environmentally friendly for regional transport and at the same time will meet the requirements of standards ČSN EN 12 663, category P2 and ČSN EN 15 227, category C I and will be friendly to road users
FINITE ELEMENT SIMULATION ANALYSIS OF STEEL TRUSS ARCH BRIDGE JACKING CONSTRUCTION
Get PDFIn this study, a spatial model of a steel truss arch bridge was established using the finite element software Midas/Civil to simulate and analyze the jacking construction process. The stress performance of the guide beam and main structure at each jacking stage was obtained. The results showed that in the first stage of jacking, the maximum stress and deflection values of the main girder were observed. The maximum stress on the upper edge of the main girder was 34.9MPa, and on the lower edge, it was -60.4MPa. The maximum deflection was -35.88mm. The maximum stress in the guide beam occurred during the jacking process and was -53.2MPa, corresponding to the cross-section at the root of the guide beam. The maximum deflection of the guide beam occurred in the maximum cantilever state and was -30.79mm. During the arch rib jacking process, the maximum stress was -49.4MPa. Both the maximum stress and deflection values were within the allowable range, indicating that the structure was in a safe state. This study provides a reference for similar bridge jacking construction projects
Femtosecond laser processing of advanced technical materials
Get PDFUltra-short pulsed laser ablation may be used for high-precision machining with very low thermal influence on the processed materials. Due to this reason, lasers are increasingly used for processing of advanced materials, such as titanium alloys, nickel-based alloys or steel, every year. In this study, four advanced technical materials were analysed and compared under femtosecond laser irradiation with three different wavelengths. The main laser-material interaction parameters were identified, namely the ablation threshold and removal efficiency parameters. Higher removal rates were found for Ti6Al4V alloy with all three harmonic wavelengths. To increase process productivity, a method of increasing the repetition rate and scanning speed was presented. With the maximum repetition rate, the productivity increased five-fold with a similar removed depth and surface quality. Finally, the suitability of the identified parameters with regard to quality and productivity was demonstrated for fabrication of two complex structures – honeycomb and dot – which has the potential to improve friction properties of advanced materials